胸部CR的低剂量投照条件及影像质量研究

Study of Low Dose Exposure Condition and Image Quality with Chest Computed Radiography

目的:探讨降低胸部计算机X线摄影(CR)的辐射剂量并获得优良影像质量的投照条件。方法:采用不同的管电压(kVp)、管电量(mAs)、焦片距(FFD),用自动曝光控制(AEC)方式对X线检测水模和体模曝光,探测体表空气照射量;测试空间分辨率和密度分辨率及灵敏度;用视觉观测和测量胶片密度方式评价人体胸部影像质量。结果:不同的管电压和胶片距与入射体表剂量(ESD)相关,管电压越高、胶片距越远,则ESD越低;一定范围内管电量的大小对影像分辨率没有影响,但对影像噪声有影响。低剂量CR胸部照片测试密度值及视觉评价效果达到了优良的影像密度和诊断学评价的要求。结论:胸部CR投照条件应用高电压120kVp、FFD为150cm、AEC减挡曝光及正确调节CR胸部影像处理参数,可有效降低受检者辐射剂量并获得优良的影像质量。

Objective To investigate the best exposure condition for reducing the radiation dose of the chest radiography and obtaining the good quality of images. Methods With different tube voltage （kVp）, tube current time （mAs）, and focus-film distance（FFD） adopted, X-ray detecting phantom was exposed by means of automatic exposure control（AEC）. The dosage absorbed in skin was detected; Spatial resolution capacity, low contrast resolution capacity and low contrast sensitive degree were tested. The space and density resolution capacity were tested. The chest image quality was appraised by the way of visual observation and the measure of film density. Results The different kVp and FFD were related to the emitting skin dose （ESD）, the higher kVp and the farther FFD follows the lower ESD; the higher or lower mAs has no effect on the image resolution capacity , but it had effect on image noise. The density value and seeing effect of chest film with low dose had reached good image density and needs of diagnostics. Conclusion Under the condition of 120 kVp high voltage, FFD150cm, AEC reduced density and adjusting to the processing parameters of the CR chest images, the radiation dosage of the chest computed radiography can be reduced efficiently and the good quality of images can be obtained.